This invention relates to speech recognition apparatus and methods.
In conventional apparatus, the processing facilities required is reduced and the speed of operation is increased by syntax selection. The apparatus is programmed to recognize first only a preselected number of words in a first group which are the words that the speaker would speak first in making any of the commands for which the apparatus is programmed. After recognition of the first word, the apparatus is programmed to recognize only a preselected number of words in a second group which may, but need not always be different from the first group, the second group of words being those which the speaker would, in correct usage, speak after the first. The recognition of a string of words making up a command thereby proceeds step-by-step in this way, with each successive word being identified from a limited group of words which the apparatus is programmed to expect the speaker to use at that point in the string. In this way, the vocabulary with which the apparatus compares a spoken word at any point in the string can be reduced, leading to a more rapid identification and a reduction in processing capacity.
While syntax selection may work satisfactorily when the speaker speaks each word in the order programmed in the apparatus and without repetition, it may break down if the speaker does not follow the prescribed procedure. It is fairly common for a speaker to be interrupted while speaking a command and, when resuming the command or dialogue, to repeat one or more words already spoken. Also, the speaker may contravene grammar and, or alternatively, syntax rules formulated for a precise written language. Where syntax selection is used, the recognition of a word when it is spoken for a first time will cause the apparatus to move onto the next succeeding step in the recognition process and will change the stored vocabulary with which the spoken words are compared. This new group of words in the stored vocabulary will not generally contain any of the words in the preceding group so the apparatus will fail to recognize the repeated word and will abort the recognition process, signalling the speaker to the effect that the command is not recognizing. Worse still, it may cause an undetected misrecognition to occur. Failure will also occur where a word is omitted or spoken in a different order from that stored in the apparatus.
In circumstances where a speaker is under pressure, it may be quite common for spoken commands not to fit the sequence in the recognition apparatus. It is, however, often in these circumstances where it is important for the recognition apparatus to identify the spoken, command the first time it is spoken, so that the command is effected without delay.